What would be the vapor pressure of water at $80$hat$(A)C$ above a solution made by dissolving $8\mathrm{.}743g$ of sodium chloride, NaCl, in $258\mathrm{.}1g$ of water? The vapor pressure of pure water at this temperature is $355\mathrm{.}1mmHg.$ Assume complete dissociation of solute.

Key Concept: Colligative properties $-$ vapor pressure lowering in the presence of an ionic salt.

Strategy:

This following Raoult's law $P=P^0{x}_{\text{s}\text{o}\text{l}\text{v}\text{e}\text{n}\text{t}}$ where $x_{\text{s}\text{o}\text{l}\text{v}\text{e}\text{n}\text{t}}=\frac{n_{\text{s}\text{o}\text{l}\text{v}\text{e}\text{n}\text{t}}}{i^{**}{n}_{\text{s}\text{o}\text{l}\text{u}\text{t}\text{e}}+n_{\text{s}\text{o}\text{l}\text{v}\text{e}\text{n}\text{t}}}.$

Use the two two masses to determine the mole fraction of solvent making sure to use the van't Hoff factor.

Use mole fraction and Raoult's law to figure out the vapor pressure.